I. Field of the Invention
The present invention relates generally to pumps and, more particularly, to a fuel pump for an internal combustion engine and, particularly, a direct injection internal combustion engine.
II. Description of Related Art
There are different types of internal combustion engines used to propel automotive vehicles. However, direct injection internal combustion engines are becoming increasingly more common due to their fuel efficiency.
In a direct injection internal combustion engine, the fuel injector is open directly to the combustion chamber rather than upstream from the intake valves as in the previously known multipoint fuel injectors. Since the fuel injectors are open directly to the cylinders or combustion chambers of the engine, the fuel injectors are subjected to high pressure. As such, it is necessary to supply fuel to the fuel injector at a pressure which is not only sufficient to overcome the pressure of the internal combustion chamber, but also to atomize the fuel injection.
In order to provide high-pressure fuel to the fuel injectors, the previously known direct injection internal combustion engines have utilized a piston pump having a piston mounted in a pump chamber. Upon the intake stroke of the piston, the piston inducts fuel into the fuel chamber from a fuel source, such as a fuel tank. Conversely, upon the compression stroke of the piston, the piston extends into the pump chamber and pumps fuel out through a one-way check valve to a fuel outlet for the pump. This fuel outlet, in turn, is connected to a fuel rail which supplies the fuel to the fuel injectors for the engine.
One disadvantage of these previously known fuel pumps for direct injection engines, however, is that the aggressive pressure profile of the pump piston causes a water hammer effect when the check valve at the pump outlet opens and closes. This water hammer effect creates excessive noise, particularly at low engine speeds where the noise is much more noticeable to occupants of the vehicle.
A still further disadvantage of these previously known pumps for direct injection engines is that it is necessary to convert the rotational force of the cam into a linear force for the pump piston. This motion conversion results in excessive power consumption by the pump. This power consumption, of course, must be sustained by the engine thus resulting in a reduced engine efficiency.
A still further disadvantage of these previously known piston pumps for direct injection engines is that the force of the cam on the pump piston may result in material fatigue and pump failure after extended operation.